(1) Field of the Invention:
This invention relates to a novel process for the synthesis of substituted cyclopropane-carboxylic esters represented by the following general formula ##STR1## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4, which may be the same or different, each stand for hydrogen atom or a hydrocarbon group, R.sup.1 and R.sup.2 or R.sub.1 and R.sup.3 may be bonded to form a ring together with the carbon atoms to which they are linked, R.sup.13 stands for an alcohol residue, and Y and Z, which may be the same or different, each stand for hydrogen or a halogen atom, and to novel intermediates leading to these esters.
Substituted cyclopropane-carboxylic esters represented by general formula [I] are valuable as insecticides or intermediates for synthesis of insecticides. Especially, allethronyl, pyrethronyl, 3-phenoxybenzyl and 5-benzyl-3-furylmethyl esters of 2,2-dimethyl-3-(2',2'-dihalogenovinyl)cyclopropane-carboxylic acids have an insecticidal activity at least several times as high as the insecticidal activity of corresponding esters of chrysanthemic acid and have a highly improved photostability, and these esters are included in pyrethrin analogues which have recently attracted attention in the art as insecticides [see European Chemical News, November 23, 39 (1973); M. Elliot et al, "Nature", 244, 456 (1973); and D. G. Brawn et al, J. Agr. Food Chem., 21, No. 5, 767 (1973)].
(2) Description of the Prior Art:
It is known in the art that the foregoing esters can be prepared by decomposing a lower alkyl ester of chrysanthemic acid with ozone and subjecting the resulting lower alkyl ester of 3-formyl-2,2-dimethyl-cyclopropane-carboxylic acid to the Wittig reaction (see Japanese patent Application Laid-Open Specification No. 47531/74).
This known process, however, is not industrially advantageous, because the starting lower alkyl ester of chrysanthemic acid is expensive and an expensive phosphorus compound should be used as a reactant.
As a result of our research works made with a view to developing a process for preparing the above esters of 2,2-dimethyl-3-(2',2'-dihalogenovinyl)cyclopropane-carboxylic acids at low costs with industrial advantages, we have now found a process in which the Wittig reaction is not utilized.